Because white papers, policy reports, and other grey literature exist outside the academic publication ecosystem, they rarely are subjected to peer review. 

Similarly, the authors of academic working papers, manuscripts, and conference presentations eventually may submit these texts for publication in refereed journals, but these works have not yet been appraised for quality.  As a result, it may more difficult to determine the credibility of grey literature than it is for traditional academic publications.  Under these conditions, authorial--individual, organizational, etc.--reputation tends to assume greater significance.  The following resources address the question of credibility, especially as it concerns think tanks.